Converting Scores Between the PANSS and SAPS/SANS Beyond the Positive/Negative Dichotomy

Abstract Background: Previous work provided conversion equations for overall indices of positive and negative symptomatology between the two most widely used scales to assess symptom severity in schizophrenia, namely the Positive and Negative Syndrome Scale (PANSS) and the Scales for the Assessment of Positive/Negative Symptoms (SAPS/SANS). Our objective was to provide such conversion equations for subdomains of positive and negative symptomatology in order to better account for the diversity of symptom profiles in schizophrenia. Method: Symptoms severity was assessed using both the PANSS and SAPS/SANS in 205 patients with schizophrenia. Two exploratory factor analyses combining items from both scales were first performed separately in the positive and negative symptom domains. For each identified factor, linear regression analyses were then conducted to obtain conversion equations from the PANSS to the SAPS/SANS and vice versa. Linear regression model estimation was performed on 80% of the data, and reliability was then evaluated on the 20% remaining data using intra-class correlation coefficient between the original and predicted scores. This procedure was repeated 100 times with random samplings for each factor cross-scale conversion.Results: Three-factor solutions were favored both in the positive and negative symptom domains. Based on the nature of items that strongly loaded on the different factors, positive factors were termed ‘Hallucinations’, ‘Delusions’ and ‘Disorganization’, while negative factors were associated with ‘Expressivity’, ‘Amotivation’ and ‘Cognition’. Intra-class correlation coefficients between the original and predicted scores were good to excellent (0.68-0.87) for all regressions, but for the cognition factor which were deemed as low (0.25, 0.26).Conclusion: The symptom subdomains identified by the decomposition of the positive and negative domains were consistent with current descriptions of symptom dimensions in schizophrenia. With the exception of the cognition subdomain, symptom severity scores can be converted with good accuracy between scales, beyond the positive/negative symptom dichotomy. Conversion equations are implemented in an R Shiny app to facilitate their use by the clinical research community.